There have been developed many types of tags for use in electronic article surveillance (EAS) systems, where the tag is mechanically attachable to an article to be monitored. To prevent unauthorized removal of the tag, various mechanical locking mechanisms have been employed to attach the tag to the article. A removal tool (typically located at the checkout counter) is provided to disengage the locking mechanism, and therefore, permit authorized removal of the tag. However, it is known that unauthorized removal of the tag can occur by defeating the locking mechanism.
To discourage unauthorized removal of the tag, it is known from U.S. Pat. No. 5,031,287 to include a breakable ink cartridge in the tag. An attempt to forcibly remove the tag from the article causes the ink cartridge to break, and, as a result, the ink splashes on the attached article. This renders the article unsuitable for use (i.e., ruins clothing) and/or renders the article readily detectable, by visual observation.
The use of ink type tags often discourages unauthorized removal of the tag. However, this approach is disadvantageous in that when the ink cartridge is broken, both the tag and the attached article are destroyed. Further, it is also possible to defeat the locking mechanism without causing the ink cartridge to break.
U.S. Pat. No. 4,686,513 discloses an alternative method of discouraging unauthorized removal whereby the state of the locking mechanism is electrically detected and an audible alarm is initiated upon detection of a disengaged state of the locking mechanism. In this way, attention is drawn towards a tag which has its locking mechanism disengaged.
By way of example, a tag is known in which an attached retaining tack is inserted into a tack clip which has a mechanical locking mechanism for holding the retaining tack in place. The tack clip is provided with an electrical switch which is arranged to enable an alarm sounder when opened. The switch is closed when the retaining tack is inserted and is opened when the retaining tack is removed. Accordingly, when the locking mechanism is disengaged (i.e., the retaining tack is removed from the tack clip), the electrical switch is opened, thereby initiating the alarm sounder located within the tag.
The above described tag, which detects the insertion of the retaining tack, is disadvantageous in that it can be disabled without opening the electrical switch. As a result, the sounder is not initiated.
Another disadvantage of the known tags is that they are vulnerable to forcible tampering (i.e., forcibly violating the tag's housing). To detect forcible tampering, U.S. Pat. No. 4,686,513 describes a tag in which an electrical switch in the tag housing is responsive to crushing forces applied to the tag housing. The electric switch is arranged to initiate an alarm sounder. In this way, attempts to crush the tag or to use a crushing force to crack open the tag's housing are detected by the electrical switch which in turn initiates an alarm sounder.
The above described tag is not however effective in detecting other types of forcible tamperings, such as, for example, stretching, bending, shock and vibrations, all of which are capable of affecting the performance of the tag. Further, the electrical switch does not detect attempts to defeat the locking mechanism as described above.
It is therefore an object of the present invention to provide an improved tag for use in an EAS system.
It is a further object of the present invention to provide a tag for use in an EAS system which detects forces applied to the tag's housing.
It is yet a further object of the present invention to provide a tag for use in an EAS system which detects forcible tamperings.
It is a still further object of the present invention to provide a tag for use in an EAS system which detects forces applied to the tag which are of the type sufficient to accomplish an unauthorized removal of the tag from an article being monitored.